I was receiving help from Michael about how to do my modeling. Here is a simple fishing led I used as a sample. we figured lofting would best get the shape I was after, though I couldnt find the control of the profile I was after as with the sweep tool. The sweep tool is limiting the "Cross Sections" I can use where the loft tool didnt.

Here is the loft with a profile I didnt care for.

So I went to the sweep, using only 2 profiles, I get my desired resulting shape.

Though I cant figure out why the asymmetrical polygon was swept at a different axis than drawn!

I was figuring out how it was picking my profiles and I guess it has something to do with the "order" and "direction" things are drawn. I had to redraw my rail in the opposite direction to get my asymmetrical polygon on the right end of the sweep. How did I rotate this polygon so the sweep rotated it?

Hi Burr, I think one thing that is causing some problems with your sweep is that you're getting the "auto-place" profile mode kicking in and it is causing some confusion there.

Auto-place mode is something that can be used for sweep which allows you to draw the sweep profiles flat on a plane and then have the sweeper move the profiles into place along the rail for you automatically.

Here's an example - say you want to create a tubular shape following the top path, with these 3 curves as the profiles:

One way to do it would be to move and rotate the profiles into place into their spots along the rail, that would look something like this:

Actually it is common for programs to need to have the profiles arranged in this way, but it can be rather inconvenient to do all that repositioning manually.

So auto-place mode is meant to allow those profiles to be selected right from their "flat" original positions and then they will get automatically moved and rotated along that rail curve for you.

The way that auto-place currently works, is that the sweeper will look at the bounding box around the rail curve. If all the profiles are outside of this bounding box, and all the profiles are planar and on a parallel plane, then it will activate auto-place mode. It so happens that your profile curves match all of this, so you are getting auto-place mode turned on. But the ordering used for auto-place mode is a left-to-right order taken from the profile's parallel plane direction, which in your case is the Right-side view. These curves are concentric from that view and not in a left-to-right order, that is why your ordering is weird.

Ok, I hope that made sense. I do want to make a more explicit control for auto-place mode in the future because it can cause problems like this when it kicks in unexpectedly.

So the solution for you in this case would be to move the profile curves up so that they are going around the rail curve instead of below them, like this:

That will turn off autoplace mode and instead the profiles will be used from exactly where they currently stand.

Or the other option if you do want to use auto-place mode is to draw your profile curves all flat next to one another in a rough left-to-right order, like in the screenshot I show above with the 3 profiles (the 2 circles and the pentagon).

Does that help explain what is happening to you in this case?

Right now your profile arrangement is kind of halfway between "direct profile positioning" and "auto-place" (because you are away from the rail) style arrangements.

> One of the questions was regarding "sweep1 picture". if you look at
> the profiles and how they stand up then look at the resulting sweep,
> you'll see the smaller polygon rotated 45 degrees.

Actually that is also caused by the auto-place mechanism getting used. The auto-place can be kind of arbitrary about which direction it decides is the "up" direction when it automatically moves things into place, I think right now it may not quite work as expected if your profiles are drawn in a different view than the Top view.

If you move your shapes up to get auto-place turned off, you should also see that strange rotation disappear at same time as well.

There definitely does need to be some work to make auto-place have a more expected "up" direction when it kicks in, but probably your best bet for now would be to move those profiles up so that mode is not kicking in at all for this thing.

> I think I read in another thread there is a selection during sweep
> that is called "twist" that is doing this.

There is a twist parameter, but it is for controlling the behavior for how paths that move around fully in 3d up and down like a roller-coaster will behave, it won't actually control anything for your flat path like in this case.

>The auto-place can be kind of arbitrary about which direction it decides is the "up" direction when it automatically moves things into place, I think right now it may not quite work as expected if your profiles are drawn in a different view than the Top view.

Just a thought, not that you dont have enough work, for your 2d objects like circles and squares and such, maybe some kind of "definition" about its rotation. I work in a cad program that does this with a 360 degree start/end point so your circle would "actually have a top" (or start point). Can this equate in nurbs creation?

Hi Burr, yup NURBS circles work in exactly that same way, they have a start and end point that touch each other.

I usually call that the "seam" of the closed curve.

If you extrude a circle into a cylinder, you'll see where the seam was, it will then become the closing seam of the cylinder surface which is closed in a similar way (start and end touching).

There is stuff in MoI that is built in to try and minimize the amount of work that you have to do for manually ensuring that the seam is in the correct place. Like for instance if you loft between 3 circles, MoI will automatically analyze them and re-configure their seam points to match nicely so that the loft does not severely torque or twist.

You can actually adjust those seam points while you are in the final stage of the loft command if you want to purposely introduce twist - before you finish Loft you'll see those points displayed inside the viewport and you can click and drag on one to reposition it.

But I'm not completely sure if that's what you are mentioning - a lot of programs also keep an extra kind of "local axis" for each object that defines a rotation for the object...

Actually in this particular case of the "up" being weird in the Sweep, it isn't really the up of the profiles that is messed up, it is the "up" that is coming from the rail curve - part of the process of sweeping involves making a set of "frames" (like an x/y/z tripod) at each point along the rail.

Ok thanks. The up has to do with a sweep calc.. Your original reply was exactly what I was talking about.

So, If i grab my polygon tool, and choose my first point, is my second click the seam? I can rotate around the origin and set the seam where I want? and if so, the properties panel you would like would have this as a "definable property", Eh!

> So, If i grab my polygon tool, and choose my first point,
> is my second click the seam?

Yup, that is correct.

> I can rotate around the origin and set the seam where I want?

Yes.

> and if so, the properties panel you would like would
> have this as a "definable property", Eh!

Yes, I would like to have it in there eventually. But it is sort of a less commonly used thing, I'm going to first focus on some basic properties like color for example. This will probably be a while longer before some of the more advanced properties get added there.